Acta Anaesthesiol Scand 2009; 53: 436–442
Printed in Singapore. All rights reserved
r 2009 The Authors
Journal compilation r 2009 The Acta Anaesthesiologica Scandinavica Foundation
ACTA ANAESTHESIOLOGICA SCANDINAVICA
doi: 10.1111/j.1399-6576.2008.01882.x
Comparison between intubation and the laryngeal mask
airway in moderately obese adults
M. ZOREMBA, H. AUST, L. EBERHART, S. BRAUNECKER and H. WULF
Department of Anaesthesia, University of Marburg, Marburg, Germany
Background: Obesity is a well-established risk factor for
perioperative pulmonary complications. Anaesthetic
drugs and the effect of obesity on respiratory mechanics
are responsible for these pathophysiological changes, but
tracheal intubation with muscle relaxation may also contribute. This study evaluates the influence of airway management, i.e. intubation vs. laryngeal mask airway (LMA),
on postoperative lung volumes and arterial oxygen saturation in the early postoperative period.
Methods: We prospectively studied 134 moderately obese
patients (BMI 30) undergoing minor peripheral surgery.
They were randomly assigned to orotracheal intubation or
LMA during general anaesthesia with mechanical ventilation. Premedication, general anaesthesia and respiratory
settings were standardized. While breathing air, we measured arterial oxygen saturation by pulse oximetry. Inspiratory and expiratory lung function was measured
preoperatively (baseline) and at 10 min, 0.5, 2 and 24 h
after extubation, with the patient supine, in a 301 head-up
position. The two groups were compared using repeatedmeasure analysis of variance (ANOVA) and t-test analysis.
Statistical significance was considered to be Po0.05.
Results: Postoperative pulmonary mechanical function
was significantly reduced in both groups compared with
preoperative values. However, within the first 24 h, lung
function tests and oxygen saturation were significantly
better in the LMA group (Po0.001; ANOVA).
Conclusions: In moderately obese patients undergoing
minor surgery, use of the LMA may be preferable to
orotracheal intubation with respect to postoperative saturation and lung function.
G
airway (LMA) does not interfere with the larynx or
the normal expiratory ‘laryngeal’ resistance, and
muscle relaxation is unnecessary. Normal diaphragmatic tonicity is thus maintained and may help to
prevent lung collapse.10,11 The aim of our study was
to evaluate the impact of the operative airway
management (LMA vs. orotracheal intubation) on
early postoperative lung function tests and pulse
oximetry values in moderately obese adults.
ENERAL anaesthesia exerts several negative
effects on lung function.1,2 Relaxation and
mechanical ventilation lead to an increased Va/Q
mismatch,3 and up to 90% of healthy adult patients
develop a measurable amount of atelectasis.4 Obesity increases the likelihood of atelectasis.5 Increased BMI correlates with loss of perioperative
functional residual capacity (FRC), expiratory reserve volume and total lung capacity, up to 50% of
preoperative values.6 These findings suggest that
adverse respiratory events are significantly more
frequent in the obese. Most of these events occur in
the post-anaesthesia care unit (PACU).7
Despite a number of controversial studies, many
anaesthetists prefer the complete airway control
that orotracheal intubation offers in the obese patient. Positive end-expiratory pressure (PEEP) and
vital capacity (VC) manoeuvres can easily be applied to prevent atelectasis, although airway irritation8 and the effects of muscle relaxation9 may be
disadvantageous. In contrast, the laryngeal mask
436
Accepted for publication 12 November 2008
r 2009 The Authors
Journal compilation r 2009 The Acta Anaesthesiologica Scandinavica Foundation
Methods
Study population
The study was approved by the Ethics Committee
of the University of Marburg. Informed written
consent was obtained from each patient. We prospectively included 134 moderately obese adult
patients (BMI 30–35, ASA II–III) scheduled for
minor peripheral surgery (Table 1). No operations
requiring abdominal insufflation (laparoscopy) or
head-down tilt were included. The minimum sur-
Intubation vs. laryngeal mask airway
gery time was set to be at least 40 min up to 120 min.
All patients were allocated on a random basis either
to the intubation or to the laryngeal mask group
s
(ProSeal Laryngeal Mask – LMA Group, Bonn,
Germany). We excluded patients who had gastrooesophageal reflux disease or a hiatus hernia, airway physical examination that may suggest the
presence of a difficult intubation, pregnancy,
asthma requiring therapy, cardiac disease associated with dyspnoea 4NYHA II or severe psychiatric disorders.
General anaesthesia
Twenty-four hours before surgery, patients were
premedicated with chlorazepat 20 mg per os. After
Fig. 1. Postoperative pulse oximetry – difference from preoperative
baseline. Changes within the study groups are significant
(Po0.0001). For abbreviations, see text.
3 min of breathing 100% oxygen by face mask,
anaesthesia was induced with fentanyl 2–3 mg/kg
and propofol 2 mg/kg, followed by a continuous
infusion of propofol 5–10 mg/kg/h. Subsequent
dosages of remifentanil (0.1–0.2 mg/kg/min) and
propofol were adjusted according to haemodynamic variables and BIS values within a range
between 40 and 60 (BIS Quatrot; Aspect Medical
Systems, Freising, Germany). To facilitate orotracheal intubation, a single dose of rocuronium
(0.5 mg/kg ideal body weight) was given; no
further neuromuscular blocking agent was given.
Patients were manually ventilated with 100% oxygen via a facemask. Respiratory settings were standardized. Immediately after intubation or
placement of the laryngeal mask, the lungs were
mechanically ventilated with a tidal volume of
8 ml/kg and the ventilation rate was adjusted to
maintain an end-tidal CO2 pressure of approximately 4–4.7 kPa. A maximum peak pressure of
30 cmH2O (25 cmH2O LMA) was set to be tolerable.
The inspiration to expiration ratio was adjusted to
1 : 1.5. A PEEP of 10 cmH2O was used in the
intubation group. The cuff pressure was continuously adjusted to 30 cmH2O (LMA 50 cmH2O).
Eighty percent oxygen in nitrogen was given during maintenance of anaesthesia. The peripheral
arterial oxygen saturation was monitored continuously by pulse oximetry. The TOF ratio was controlled via a peripheral nerve stimulator, ensuring a
TOF ratio 40.9012 before extubation. When the
patient was fully awake and breathing sponta-
Fig. 2. Postoperative expiratory lung function values – difference from preoperative baseline. Changes within the study groups are
significant (Po0.001). For abbreviations, see text.
437
M. Zoremba et al.
Fig. 3. Postoperative inspiratory lung function values – difference from preoperative baseline. Changes within the study groups are
significant (Po0.01). For abbreviations, see text.
Table 1
Spirometry and pulse oximetry
Basic data for 134 patients undergoing elective minor peripheral
surgery.
Spirometry and pulse oximetry were standardized,
and the investigator was blinded, with each patient
in a 301 head-up position13 after breathing air
without supplemental oxygen for 5 min. At the
pre-anaesthetic visit, a baseline spirometry measurement and pulse oxymetry were taken (T0) after
a thorough demonstration of the correct technique.
VC, forced vital capacity (FVC), forced expiratory
volume in 1 s (FEV1) mid-expiratory flow (MEF25–
75), peak expiratory flow (PEF), peak inspiratory
flow and the forced inspiratory vital capacity were
measured and the FEV1/FVC ratio was calculated.
At each assessment, spirometry was performed at
least three times to be able to meet the criteria of the
European Respiratory Society, and the best measurement was recorded.14 On arrival in the recovery
room, at about 5–10 min after extubation, we repeated spirometry (T1) as soon as the patient was
alert and fully cooperative (Fast Track Score 410);15
pain and dyspnoea during coughing were assessed
using the Fast Track Score (410)15 before and, if
necessary, after analgesic therapy. All patients met
this criterion within 20 min of extubation.
Spirometry and pulse oximetry assessments
were repeated in the PACU at 0.5 h (T2), 2 h (T3)
and 24 h (T4) after extubation. Before each measurement, all patients were free from pain during
coughing and had a Fast Track Score 410. Overall
piritramide consumption was documented within
the first 24 postoperative hours. Factors that interfered with breathing (e.g. pain, shivering) were
Age (years)
BMI
Surgery time (min.)
Postoperative pritramide(mg)
consumption (within 24 h)
Knee arthroscopy
Minor breast surgery
TUR-prostata
Hand surgery
Intubation
(n 5 67)
Laryngeal mask
(n 5 67)
53
32
81
10
49
30
89
11
(SD
(SD
(SD
(SD
12)
3.7)
21)
5.9)
n 5 16
n 5 35
n59
n57
(SD
(SD
(SD
(SD
12)
3.2)
19)
6.3)
n 5 12
n 5 41
n 5 11
n53
neously, the trachea was extubated, without
previous suction, in a head-up position, with a
positive pressure of 10 cmH2O, using 100%
O2. Patients were transferred to the PACU, while
breathing room air during transport. The
peripheral arterial oxygen saturation was continuously monitored by pulse oximetry. Each patient
was placed in the head-up position during the
PACU stay.
Postoperative pain management
Both groups received basic non-opoid analgesia
with intravenous (i.v.) paracetamol 1 g and metamizol 1 g i.v. Analgesia was supplemented with
intermittent piritramide (i.v.) application when the
visual analogue scale (VAS) was 44.
438
eliminated or at least minimized to produce reliable measurements.
Statistical analysis
We tested the null hypothesis (H0) that postoperative
pulse oximetry values were comparable to preoperative values. The postoperative values were calculated as a percentage of preoperative. To compare the
study groups at each measurement point, we performed Student’s t-test with a type-I error of 5%
(Table 3). We also performed a repeated-measure
analysis of variance within the study groups during
the first 24 postoperative hours (Figs 1–3). H0 was
rejected at an adjusted P of o0.0125 due to multiple
testing. One hundred and thirty four patients were
included with four values each. The results were all
analysed using StatView 4.57 for Windows (Abacus
Software, Heidelberg, Germany) and expressed as
mean standard deviation (SD).
ITN, intubation group; LMA, laryngeal mask airway; , NS, no significance for further abbreviations see text.
(1) ITN
97.2% (SD 1.1) 96.7% (SD 1.5) 3.56 l (SD1.1) 2.77 l (SD 0.9) 5.71 l (SD 2.4) 2.79 l (SD 1.2) 5.22 l (SD 2.1) 3.50 l (SD 1.5) 1.35l (SD 0.7) 3.48 l (SD 1.3) 3.34 l (SD 1.7)
(2) LMA
97.5% (SD 1)
96.9% (SD 1.2) 3.62 l (SD 1) 2.79 l (SD 0.8) 5.76l (SD 2.2) 2.72l (SD 1.2) 5.27l (SD 2.0) 3.61 l (SD 1.4) 1.16l (SD 0.6) 3.41l (SD 1.1) 3.08 l (SD 1.3)
t-test Po0.05 NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
FEV 1
FVC
SpO2 after
premed.
SpO2 before
premed.
Preoperative pulse oximetry and lung function values (baseline 5 100%).
Table 2
PEF
MEF 25-75
MEF 75
MEF 50
MEF 25
FIVC
PIF
Intubation vs. laryngeal mask airway
Results
We recruited 162 patients; the mean duration of
surgery was 80 (SD 20) min, range 40–120 min.
Acceptable ventilation was achieved in all, but five
subjects declined to continue with the protocol.
Measurements were unsatisfactory in 16 (nine in
the LMA group, and seven in the intubation group),
in whom the Fast Track Score was o10 within
20 min of surgery. Laryngo-/bronchospasm occurred
in four patients; three were in the intubation group
(NS). Placement of the laryngeal mask was unsatisfactory in three patients, who were excluded from
the study. Reversal of muscle relaxation was not
necessary in any patient. Thus, we present data for
134 patients with 67 individuals per group (Table 1).
Pulse oximetry
Preoperative saturations were within the normal
range and did not differ between the study groups
(Table 2). In both groups, the lowest values were
found immediately after extubation in the PACU after
achieving a Fast Track Score 410. Oxygen saturation
decreased more in the intubation group at all stages
than in the LMA group (Fig. 1, Table 3; Po0.0001).
Spirometry measurements
Preoperative inspiratory and expiratory spirometric
values were within the normal range (Table 2). Postoperatively, the LMA group fared significantly better
(Po0.01) (Fig. 2, Table 3). However, throughout the
439
M. Zoremba et al.
Table 3
Postoperative pulse oximetry and lung function values.
Intubation
SpO2 after surgery
T 0.5 h
T 2h
T 24 h
FVC after surgery
T 0.5 h
T 2h
T 24 h
FEV1 after surgery
T 0.5 h
T 2h
T24 h
PEF after surgery
T 0.5 h
T 2h
T24 h
MEF 25-75 after surgery
T 0.5 h
T 2h
T 24 h
MEF 75 after surgery
T 0.5 h
T2 h
T24 h
MEF 50 after surgery
T 0.5 h
T 2h
T 24 h
MEF 25 after surgery
T 0.5 h
T2 h
T24 h
FIVC after surgery
T 0.5 h
T 2h
T 24 h
PIF after surgery
T 0.5 h
T 2h
T24 h
90.3%
92.4%
93.6%
95.0%
2.33 l
2.50 l
2.62 l
2.91 l
1.62 l
1.76 l
1.89 l
2.25 l
2.83 l
2.98 l
3.43 l
4.84 l
1.52 l
1.63 l
1.79 l
2.32 l
2.60 l
2.73 l
3.16 l
4.41 l
1.90 l
2.08 l
2.24 l
2.91 l
0.76 l
0.77 l
0.83 l
1.09 l
2.14 l
2.26 l
2.37 l
3.03 l
1.57 l
1.73 l
1.89 l
2.57 l
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
2.8)
2.2)
2.3)
1.8)
0.38)
0.40)
0.42)
0.41)
0,27)
0.33)
0.36)
0.36)
0.62)
0.65)
0.72)
1.05)
0.33)
0.40)
0.48)
0.51)
0.62)
0.65)
0.79)
1.05)
0.45)
0.56)
0.60)
0.75)
0.18)
0.19)
0.23)
0.25)
0.57)
0.63)
0.64)
0.72)
0.36)
0.45)
0.53)
0.71)
Laryngeal mask
P-value (t-test)
93.5%
94.7%
95.2%
96.5%
2.62 l
2.78 l
2.93 l
3.37 l
1.93 l
2.18 l
2.20 l
2.58 l
3.74 l
3.91 l
4.10 l
5.24 l
1.79 l
1.92 l
2.05 l
2.43 l
3.57 l
3.71 l
3.84 l
4.66 l
2.37 l
2.56 l
2.67 l
3.13 l
0.83 l
0.85 l
0.91 l
1.10 l
2.35 l
2.60 l
2.77 l
3.25 l
1.71 l
1.99 l
2.10 l
2.81 l
o0.0001
o0.0001
0.0005
0.0002
0.0203
0.0150
0.0075
o0.0001
0.0010
0.0015
0.0016
0.0003
0.0001
o0.0001
0.0033
0.1751(NS)
0.0028
0.0033
0.0072
0.0950 (NS)
o0.0001
o0.0001
0.0035
0.2327 (NS)
0.0082
0.0133
0.0275
0.4180 (NS)
0.0182
0.0009
0.0006
0.0076
0.0850
0.0140
0.0022
0.1596 (NS)
0.0218
0.0128
0.0271
0.0065
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
(SD
2.2)
2.1)
2.1)
1.7)
0.42)
0.41)
0.44)
0.43)
0.36)
0.37)
0.37)
0.40)
0.81)
0.84)
0.85)
1.12)
0.35)
0.40)
0.43)
0.51)
0.89)
1.01
0.94)
1.10)
0.56)
0.66)
0.64)
0.65)
0.17)
0.18)
0.19)
0.19)
0.50)
0.52)
0.57)
0.56)
0.31)
0.25)
0.42)
0.61)
P-value 5 t-test analysis for each measurement point tested on a significance level of Po0.05.
For abbreviations, see text.
measurement period, inspiratory and expiratory lung
volumes improved only moderately during the stay
in the PACU. Even on the first day after surgery, lung
function was reduced by up to 25% of baseline, and
inspiratory and expiratory lung volumes were significantly reduced (Po0.01; Fig. 2). Both study groups
showed a similar recovery pattern over the course of
the observation period. t-test analysis confirmed the
advantage of the LMA in the PACU at all measurement points (Table 3). The difference ceased to be
significant at 24 h post-surgery.
Postoperative management
No patient suffered from untreatable postoperative
pain. The maximum postoperative pain score on a
440
VAS scale before analgesia was 6 (both groups).
Opioid consumption within 24 h was comparable
in both groups (Table 2). At each measurement
point, every patient was acceptably awake, and
free of pain, shivering or nausea.
Discussion
Obesity has considerable negative effects on lung
function in the perioperative period, due to a loss of
FRC, atelectasis and increased desaturation. Most
pulmonary complications occur in the immediate
postoperative period, for which there are little data.
Although healthy patients may easily compensate
for the postoperative impairment of lung function, in
Intubation vs. laryngeal mask airway
the obese and those with pre-existing lung disease,
postoperative lung volumes and oxygenation are
likely to be significantly affected.
As reported previously 6,16, the maximum
changes in spirometry and arterial saturation occurred during the first assessment after extubation.
Further measurements in the PACU showed only a
slight recovery of postoperative inspiratory and
expiratory lung functions within the first 2 h. We
attribute this to impaired respiratory mechanics,
obesity and atelectasis formation induced by general anaesthesia in the supine position.
Our data show that the use of an LMA during
minor peripheral surgery confers advantages for
moderately obese adults in terms of early postoperative lung function and pulse oximetry saturation.
Some anaesthetists may be reluctant to use the LMA
in moderately obese adults; in our study, ventilation
was acceptable in all patients included, and previous
studies with sufficient power have confirmed this.17,18
Most of the problems in the LMA group were caused
by inaccurate placement of the laryngeal mask with
consecutive leakage. Our findings suggest that there is
no difference in major adverse events (e.g. pulmonary
aspiration) between our study populations. No aspiration occurred during the study period in either group,
although patients with increased risk were excluded.
While there is no doubt that orotracheal intubation is
the gold standard for these cases, there are no data to
suggest that the use of the laryngeal mask to ventilate
moderately obese adults is associated with an increased risk for pulmonary aspiration. There was no
difference in the incidence of laryngospasm between
the groups, although our study lacks the power to
demonstrate such a difference.
Orotracheal intubation generates greater airway
irritation with subsequent tissue oedema,8 which
could mimic obstructive lung disease. It is uncertain whether this effect contributes to our findings
to any significant extent, because the surgical time
did not exceed 120 min and the cuff pressure was
continuously adjusted to 30 cmH2O in the intubation group and 50 cmH2O in the LMA group.
Some patients receiving intraoperative muscle
relaxants have a residual neuromuscular block after
extubation, which may affect the reliability of the
study. To reduce this possibility, the minimum surgery time was 40 min and no additional dose of any
muscle relaxant was given, and extubation was
performed only after recovery of the train-of-four
ratio to 40.90.12 In view of our measured postoperative inspiratory lung volumes, which showed
a similar postoperative recovery in both groups,
residual neuromuscular block can be almost entirely
excluded. However, our data suggest that the initial
muscle relaxation to facilitate orotracheal intubation
causes a significant amount of atelectasis. Previous
studies indicate that muscle relaxation develop atelectasis by compression of lung tissue rather than
by resorption of gas.9,10 This compression with consequent small airway collapse persists up to 24 h
after surgery, shown by a significantly decreased
MEF25 in the intubation group, in spite of use of an
intraoperative continuous PEEP of 10 cmH2O Hg to
prevent atelectasis.19–21 The decreases in VC, FVC,
FEV1, MEF25–75 and PEF followed the same
pattern, and the FEV1/FVC ratio did not change.
This suggests a restrictive pattern of respiratory
compromise in the immediate postoperative period,
as described previously.16,22–25
The postoperative impairment of spirometry
measurements was probably not caused by a lack
of cooperation, because all the patients in this study
were alert and fully compliant within 20 min of
extubation, and any pain had been treated. Any
lack of cooperation and insufficient pain management6,16,22 would be expected to affect the whole
study population to a comparable degree. Nevertheless, our pulse oximetry and spirometry findings
indicate that airway management has a greater
impact on postoperative lung volumes than previously assumed. The decreased inspiratory capacity might affect the ability to cough effectively, and
thus predispose to respiratory complications.
Our findings suggest that moderately obese
patients who are scheduled for minor peripheral
surgery may benefit from use of the laryngeal mask
rather than orotracheal intubation. It is not clear
whether this is related to the initial muscle relaxation to facilitate orotracheal intubation, or a specific
effect of the LMA. It is also unclear whether this
form of airway management reduces postoperative
complications; larger studies are needed.
Limitations
One major limitation factor is the preselection of our
patients. Only moderately obese patients scheduled
for minor peripheral surgery were included. No
operations with abdominal insufflations (laparoscopy) or head-down tilt were included. In addition,
we excluded patients with gastro-oesophageal reflux
disease or a hiatus hernia. Furthermore, the potential
for a selection bias was minimized by the support of
anesthetists not involved in the study, who were
441
M. Zoremba et al.
responsible for giving patients preoperative information. Additionally, postoperative spirometry was performed by trained nurses who were unaware of the
study hypothesis and were not involved in this study.
Our findings do not allow us to suggest that the
LMA should be used routinely for these cases. The
primary aim of our study was to examine the
potential of different airway regimes for modifying
spirometrically measured lung volumes in the immediate postoperative period, when the impacts of
surgical trauma and anaesthesia are most likely to
trigger postoperative pulmonary morbidity. The
reduction of postoperative lung function was significantly greater in the intubation group than in
the LMA group. We conclude that the LMA may be
considered as an alternative to orotracheal intubation for moderately obese patients undergoing
minor surgery. A larger study population is required, however, in order to establish the LMA as
the standard procedure for our study population.
References
1. Marshall BE, Wyche Jr. MQ Hypoxemia during and after
anesthesia. Anesthesiology 1972; 37: 178–209.
2. Moller JT, Johannessen NW, Berg H, Esperesen K, Larsen
LE. Hypoxaemia during anaesthesia: an observer study. Br
J Anaesth 1991; 66: 437–44.
3. Lundquist H, Hedenstierna G, Strandberg A, Tokics L,
Bismar B. CT assessment of dependent lung densities in
man during general anaesthesia. Acta Radiol 1995; 36: 626–32.
4. Gunnarsson L, Tokics L, Gustavsson H, Hedenstierna G.
Influence of age on atelectasis formation and gas exchange
impairment during general anesthesia. Br J Anaesth 1991;
66: 423–32.
5. Eichenberger A, Proietti S, Wicky S, Frascarolo P, Suter M,
Spahn DR, Magnusson L. Morbid obesity and postoperative pulmonary atelectasis: an underestimated problem.
Anesth Analg 2002; 95: 1788–92.
6. Von Ungern-Sternberg BS, Regli A, Schneider MC, Kunz F,
Reber A. Effect of obesity and site of surgery on perioperative lung volumes. Br J Anaesth 2004; 92: 202–7.
7. Benoit Z, Wicky S, Fischer JF, Frascarolo P, Chapuis C,
Spahn DR, Magnusson L. The effect of increased FIO2
before tracheal extubation on postoperative atelectasis.
Anesth Analg 2002; 95: 1777–81.
8. Kim E, Bishop MJ. Endotracheal intubation, but not laryngeal mask airway insertion, produces reversible bronchoconstriction. Anaesthesiology 1999; 90: 391–4.
9. Tokics L, Hedenstierna G, Strandberg A, Brismar B, Lundquist H. Lung collapse and gas exchange during general
anesthesia: effects of spontaneous breathing, muscle paralysis, and positive end-expiratory pressure. Anesthesiology 1987; 66: 157–67.
10. Brismar B, Hedenstierna G, Lundquist H, Strandberg A,
Svensson L, Tokics L. Pulmonary densities during anaesthesia with muscular relaxation – a proposal of atelectasis.
Anaesthesiology 1985; 62: 422–8.
442
11. Pelosi P, Ravagnan I, Giurati G, Panigada M, Bottino N,
Tredici S, Eccher G, Gattinoni L. Positive end-expiratory
pressure improves respiratory function in obese but not in
normal subjects during anesthesia and paralysis. Anesthesiology 1999; 91: 1221–31.
12. Eikermann M, Groeben H, Hüsing J, Peters J. Accelerometry of adductor pollicis muscle predicts recovery of respiratory function from neuromuscular blockade. Anesthesiology
2003; 98: 1333–7.
13. Gudmundson G, Cerveny M, Shasby DM. Spirometric
values in obese individuals, effect on body position. Am J
Respir Crit Care Med 1997; 155: 998–9.
14. Standardized lung function testing. Offcial statement of the
European Respiratory Society. Eur Respir J 1993; 16 (Suppl.):
1–100.
15. White PF, Song D. New criteria for fast-tracking after
outpatient anesthesia: a comparison with the modified
Aldrete’s scoring system. Anesth Analg 1999; 88: 1069–72.
16. von Ungern-Sternberg BS, Regli A, Reber A, Schneider MC.
Comparison of perioperative spirometric data following
spinal or general anaesthesia in normal-weight and overweight gynaecological patients. Acta Anaesthesiol Scand
2005; 49: 940–8.
17. Verghese C, Brimacombe JR. Survey of laryngeal mask
airway usage in 11,910 patients: safety and efficiacy for
conventional and nonconventional usage. Anaesth Analg
1996; 82: 129–33.
18. Voyagis GS, Photakis D, Kellari A, Kostani E, Kaklis S,
Secha-Dousaitou PN, Tsakiropoulou-Alexiou H. The laryngeal mask airway: a surwey of its usage in 1,096 patients.
Minerva Anestesiol 1996; 62: 277–80.
19. Brismar B, Hedenstierna G, Lundquist H, Strandberg A,
Svensson L, Tokics L. Pulmonary densities during anesthesia with muscular relaxation- aproposal of atelectasis.
Anesthesiology 1985; 62: 422–8.
20. Tokics L, Hedenstierna G, Strandberg A, Brismar B, Lundquist H. Lung collapse and gas exchange during general
anesthesia: effects of spontaneous breathing, muscle paralysis, and positive end-expiratory pressure. Anesthesiology 1987; 66: 157–67.
21. Coussa M, Proietti S, Schnyder P, Frascarolo P, Suter M,
Spahn DR, Magnusson L. Prevention of atelectasis formation during the induction of general anesthesia in morbidly
obese patients. Anesth Analg 2004; 98: 1491–5.
22. von Ungern-Sternberg BS, Regli A, Bucher E, Reber A,
Schneider MC. The effect of epidural analgesia in labour on
maternal respiratory function. Anaesthesia 2004; 59: 350–3.
23. Meyers JR, Lembeck L, O’Kane H, Baue AE. Changes in
functional residual capacity of the lung after operation.
Arch Surg 1975; 110: 576–82.
24. Alexander JL, Spence AA, Parikh RK, Stuart B. The role of
airway closure in postoperative hypoxemia. Br J Anaesth
1973; 5: 34–40.
25. Craig D. Postoperative recovery of pulmonary function.
Anesth Analg 1981; 60: 46–52.
Address:
Martin Zoremba
Department of Anaesthesia
University of Marburg
Baldingerstraße
D-35033 Marburg
Germany
e-mail: [email protected]